What is a session in Google Analytics?
How does Google Analytics count a session?
Think of a session as a visit with a stopwatch. A person arrives and Analytics opens a session. Google's documentation says it records a session_start event and gives the session an ID based on its start time1. They click around. They go quiet for long enough and the session closes. They come back later and a new one opens.
Two things follow.
First, the number of sessions is not the number of people. One person with three visits makes three sessions.
Second, the end of a session is a rule, not a fact about the person. Change the inactivity timeout and the totals move, though nobody behaved any differently.
Why does the session count matter?
Sessions are the bottom of many fractions. Shops often calculate conversion rate as orders divided by sessions. Engagement rate and bounce rate in GA4 are built on sessions too. If the denominator shifts, the rate shifts with it.
That is why a traffic report can look worse while the shop is doing fine. Or better, while it is not. Before you read a change as customer behaviour, check whether the counting changed.
Sessions also tell you little about money. A session is a unit of activity, not a unit of revenue. How credit for a sale is split between visits is a separate question, covered under attribution.
For ZFD: We treat a session total as a counting result and check how it was counted before we compare periods. It is one of the checks in an ecommerce tracking audit. For what the tool counts and what it leaves out, see what GA4 counts and what it doesn't.
Easily confused with
Session vs Users
A user is a person or device. A session is one period of activity by that user. One user can have many sessions.
Session vs Pageviews
A session can contain one pageview or dozens.
Session vs Visit
Another word for the same idea. The name differs by tool, and so can the rules.
Session vs Conversion
An action you care about, such as a purchase. A session may contain one, many or none.
FAQ
Is a session the same as a visitor?
No. A visitor is a person or device. A session is one stretch of activity. One visitor can produce many sessions.
Can I change when a session ends?
Yes. Google's documentation says the default 30-minute timeout can be changed in the tag settings for web, and in code for apps1. Change it and your totals move, so note the date.
Why do session counts differ between two tools?
Each tool opens and closes sessions by its own rules. Two honest tools can give two different totals for the same traffic.
Sources
- About Analytics sessions - Analytics HelpPrimary source
Let’s find what’s actually working.
Next step. See what your traffic and sales look like on explicit assumptions. Use the Is your ROAS real? calculator.